| Due to the shortage of water resources and the serious pollution of water,people have paid more attention to the recovery and reuse of sewage.The wastewater treatment in our country mostly adopts the process represented by activated sludge,which can't effectively remove the pollutants in the water,so there are still many organic substances in the secondary effluent.As a conventional water treatment process,coagulation is often used in advanced treatment of wastewater.But the removal efficiency of pollutants is very limited.Coagulation often combines with other processes t o improve the removal of pollutants in the secondary effluent.In this experiment,with the aim of wastewater reuse,the treatment efficiency of potassium ferrate and Fe(VI)/Fe(II)systems on pollutants in secondary effluent was studied;at the same time,we made sludge sorbents from surplus sludge from water supply plants,and studied the treatment efficiency of the sludge sorbents in the secondary effluent contaminants;At last,the treatment efficiency of various contaminants in the secondary effluent with the combination of oxidiz ing agent and adsorbent to enhance coagulation was verified in a small coagulation-sedimentationfiltration pilot plant.The experimental results show that potassium ferrate can play a good role in oxidation and coagulation,and convert macromolecule organics into small molecule organics.When the ferrate dosage was 10 mg/L,the removal rate of turbidity was 74.5%,the removal rates of COD and DOC were 50% and 27.7%,and the removal rates of ammonia nitrogen and total nitrogen were 6.5% and 24.2%,respectively.Potassium ferrate also has a good removal effect on micro-pollutants,but the removal rates of atenolol,gemfibrozil,carbamazepine and ibuprofen are low,which were 25%,26.7%,19.7% and 14.6%,respectively.In the Fe(VI)/Fe(II)system,when the dosages of Fe(VI)and Fe(II)are 5mg/L and 1mg/L,respectively,the removal of various pollutants can be greatly enhanced.The removal rate of turbidity was 90%,the COD and DOC removal rates were 60% and 32%,and the removal rates of ammonia nitrogen and total nitrogen were 32% and 35%,respectively.The sludge sorbents made from the sludge of water supply plant also had good removal effect on pollutants.When the sludge sorbent dosage was 2g/L,the DOC removal rate was 34.7%,and the removal rates of ammonia nitrogen and TN were 23% and 15.5%,respectively.The removal rates of chlortetracycline,oxytetracycline,enrofloxacin,norfloxacin,sulfamethazine,sulfamethoxamine and carbamazepine were over 90%.When different coagulants and sludge adsorbents were used together,and the dosage of sludge was 1 g/L,the PAC and Fe Cl3 dosages were 40 mg/L and 50 mg/L,the turbidity removal rates were 82% and 78%,respectively.The TP removal rates were 54% and 62%,respectively,which was significantly greater than the turbidity and TP removal rates when 1 g/L sludge sorbent was added alone.When the reflux ratio of the Densadeg was controlled to 50%,the TP,turbidity and DOC had the best removal efficiency,and the removal rates were 74%,94%,and 47%,respectively.Through the coagulation precipitation filtration device,and the reflux ratio was controlled to 50%,the Fe(VI)and Fe(II)dosages were 5mg/L and 1mg/L,and the sludge sorbent dosage was 1g/L.The water flow rate was 1L/h,continuous operation for 10 days,the average removal rate of turbidity could reach more than 90%,the average removal rates of TP,COD,UV254 can reach more than 70%;and for chlortetracycline,oxytetracycline,bezafibrate,Enrofloxacin,Norfloxacin,Atenolol,Sulfamethazine,sulfamethoxazole,gemfibrozil,carbamazepine,the removal rates could reach more than 90%.The results of genotoxicity showed that the removal rate of genetic toxicity of secondary effluent was 58.8%,when 5 mg/L of ferrate was added alone,and when the Fe(VI)and Fe(II)dosages were 5mg/L and 1mg/L,respectively,the genetic toxicity removal rate was 82.8%;addition of 1 g/L sludge sorbent alone resulted in a genetic toxicity removal rate of 80.4%;The genotoxicity removal rate reached 97% after continuous flow test of coagulation-precipitation-filtration,which indicated that enhanced coagulation with potassium ferrate and sludge adsorbent had significant effect on reducing the genotoxicity of sewage. |
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